Yttrium-iron-garnet (YIG) spheres are used in high frequency filter, oscillator and other devices that are tuned to a resonant frequency by a magnetic field. Thus, a YIG device is a filter, oscillator, parametric amplifier, or other device that uses a YIG crystal in combination with a variable magnetic field to achieve wide-band tuning. YIG devices advantageously exhibit a high resonant frequency, a wide tuning range, linear tuning characteristics and spectral purity. YIG devices are typically supplied as a YIG sphere placed in a magnetic circuit, such as a gap between two magnetic pole faces. The resonant frequency is a function of the location of the YIG sphere, and under static conditions the gap from the YIG sphere to the magnetic field source is fixed. However, in a vibrating environment small dynamic mechanical distortions occur in the YIG device resulting in changes in the resonant frequency of the YIG device. The YIG device is particularly sensitive to vibrations experienced in the axis of the magnetic field, and in certain embodiments particularly so in the central portion of the device. The shifts in resonant frequency result in high frequency signal degradation, such as phase noise degradation. The resonant frequency may further drift with temperature, and thus heat generated by a YIG device must be channeled away to prevent resonant frequency drift.
In order to prevent vibration of the YIG device, a mechanically isolating material such as a cellular silicone may be used to mount the YIG device, resulting in less mechanical energy being transmitted to the YIG device, thus reducing signal degradation. Experiments performed by the inventors show that about a 20 dB reduction in phase noise degradation at a 1 KHz offset from the carrier and 10 dB reduction at 10 KHz offset is achieved by mounting the YIG device in a cellular silicone with a compression force deflection at 25% deflection of less than 5 pounds per square inch (PSI).
Unfortunately, typically good mechanical isolation results in poor thermal conductivity between the YIG device and the enclosure for the YIG device. As indicated above, the YIG device changes exhibits an uncontrolled increase in temperature in the absence of good thermal conduction, resulting in undesired electrical performance, particularly resonance frequency drift, damage, and decreased operating lifespan.
U.S. Pat. No. 4,651,116 issued Mar. 17, 1987 to Schloemann, the entire contents of which is incorporated herein by reference, is addressed to a vibration insensitive magnetically tuned resonant circuit comprising a nonmagnetic collar or a combination of a raised peripheral edge portion and a raised central inner portion. The requirement for additional structures within the YIG device adds to cost, and does not allow for the selection of commercially available YIG devices.
U.S. Pat. No. 4,758,926 issued Jul. 19, 1988 to Herrel et al., the entire contents of which is incorporated herein by reference, is addressed to a fluid-cooled integrated circuit package. The requirement for a cooling fluid adds to cost, and may not be feasible in many deployments. Furthermore, fluid cooling does not address the issue of vibration.
U.S. Pat. No. 5,930,115 issued Jul. 27, 1999 to Tracy et al., the entire contents of which is incorporated herein by reference, is addressed to an apparatus, method and system for thermal management of a semiconductor device. The mechanical isolation described is arranged to prevent physical contact and resultant damage to an unpackaged semiconductor die mounted directly on a printed circuit substrate, and thus is ineffective for mechanically isolating a YIG device from vibration of the enclosure surrounding the YIG device.
The above has been detailed in relation to a YIG device, however this is not meant to be limiting in any way, and is equally applicable to any electro-magnetic device which generates heat and is variant responsive to changing mechanical forces.
What is desired, and not supplied by the prior art, is a means for mechanically isolating an electro-magnetic device from changing mechanical forces experienced by a surrounding chassis while providing good thermal management of the electro-magnetic device.